/Engine/Source/Editor/UnrealEd/Classes/Editor/UnrealEdEngine.h
Attempt to unhide all actors and BSP models by setting their bHiddenEdTemporary flags to false if they are true. Note: Will not unhide actors/BSP hidden by higher priority visibility settings, such as bHiddenEdGroup, but also will not modify/dirty actors/BSP.
virtual void edactUnHideAll ( [UWorld](API\Runtime\Engine\Engine\UWorld) * InWorld )